Sorry for the delayed post. Been working and havent had much free time. But the Blazer still overheats sitting at an idle with the AC on and I can't figure it out. Having changed my fan clutch, flushed my system, cleaned the radiator, and replaced my upper and lower hoses.. I'm out of options. I realize its only at an idle, but overheating is overheating lol what are my next options anyone?

 

You have both upper & lower fan shrouds on, right?!
If you look into the rad, how does it look? Clean or off color possibly bunged up below? (Where you can't see.)
On the front of the rad are the fins pretty much straight, not bent over? No air flow issues?

 

u got her pretty hot. not a good ideal to let idle like that when its hot outside for any amount of time. mostlikely u have air in the system. u have changed everything. hope u havnt damaged the engine

 

These engines (so I've heard) are meant to run at 195. That's still pretty freaking hot IMO. I'd like it to run at half that, but more HP = more heat in my case.
I agree on the air trap/bubble but if that were the case it should heat up quicker.
Hows the heat in the cab? Hot when you turn it up to heat?
If not then I'd look at an air bubble or heater core plugged.
Maybe take it to a shop to get the cooling system evacuated properly.

 

Im haveing a simular problem with my blazer.I noticed welll sitting at trains in about 70-80 degree days with the a/c on it would try to over heat 230 or so.So one time i happen to put the truck in nuteral and notice the gauge dropped 15-18 degress well still sitting there

 

Probably because the engine is revving higher & that means more air across the rad etc & the water pump is running faster as well.
Remember, the trans fluid & oil also get cooled by the rad.

 

You said you cleaned the system but I'm just thinking of some of the bad stories about DexCool & things getting bunged up in the rad & heater core from old, non maintained coolant.
As you drive the coolant has enough flow to get over the plugged passages, as you idle the levels drop & it can't get over the plugged passages - over heating.
Just thinking outloud.

 

From what the previous owner told me, he had a newerish engine put in 3 years ago, and said he had all new fluid put on following the new engine. The old coolant didn't have any debris in it nor did it seem chunk or miscolored? Don't know if that bit of information could help? Just wondering if maybe the t-stat i bought might be bad? Possible?

 

Could be a bad stat, a new one is $15 for a Fail Safe.
Keep in mind & this holds especially true for thermostats - new does not mean right! They have a bad rep for being bad right out of the box.

 

Alrighty, looks like im gonna go pick myself up another one then. lol I still have the old one, is there a way to test the old one to see if it was even bad to begin with?